Generally, a windmill is a device for generating power using the force of an air flow which is spontaneously generated in the Earth's atmosphere, and then dissipated. Such a windmill includes at least one blade adapted to receive a lift force caused by the force of a wind so that it rotates.
Such a windmill blade should have a construction capable of generating a lift force even when it receives a weak wind force, while rotating continuously and smoothly without being damaged by a strong wind force. In order to generate a lift force with a weak wind force, the windmill blade should have a large area. On the other hand, in order to prevent the windmill blade from being damaged by a strong wind force, the windmill blade should have a small area. Thus, the windmill blade should satisfy these two opposing conditions.
In spite of such a fact, early windmill blades had a large surface area in order to receive an increased amount of wind force. For this reason, they were often damaged by a strong wind force. However, windmill blades recently developed have a cured structure having a certain skew angle, so that they have an improved wind force utilization efficiency without being damaged by a strong wind force.
However, all of these conventional windmill blades have a structural drawback in that they cannot cope with a variation in wind force. In order to solve this problem, a new windmill blade has been proposed which is capable of varying its angle depending on a variation in the velocity of wind, thereby varying the area receiving the force of the wind.
In such a windmill blade capable of adjusting the angle thereof, the angle adjustment can be easily achieved when the wind force is weak. However, where the wind force is strong, it is difficult to adjust the angle of the blade because resistance to the wind force increases.
Referring to FIG. 32, a conventional wind power generating device is illustrated. As shown in FIG. 32, the conventional wind power generating device includes an iron tower 200 installed on the ground, and a windmill blade 210 mounted to the rear end of a rotating shaft 210A. The rotating shaft 210A is rotatably supported by a bearing 220 mounted on an upper end of the iron tower 200.
The wind power generating device also includes a power transmission unit 230 serving as means for transmitting wind power generated in accordance with the rotation of the windmill blade 210 to a device adapted to use the wind power. The power transmission unit 230 includes a transmission shaft 234 extending downwardly at a front portion of the rotating shaft 210A. The transmission shaft 234 is connected, at its upper end, with the rotating shaft 210A by an upper bevel gear 231. The lower end of the transmission shaft 234 is connected to the wind power using device by a lower bevel gear 232 supported by a support die 233 mounted to the iron tower 200 so that it can transmit wind power to the wind power using device.
However, the above mentioned conventional wind power generating device generates little wind power because it uses the single windmill blade to generate the wind power. Furthermore, there is no means for changing the direction of the windmill blade depending on a variation in the direction of wind. For this reason, the conventional wind power generating device exhibits a low efficiency of generating wind power. As a result, there is a problem in that it is impossible to obtain a large quantity of power from such a conventional device.